U.S. Pat. No. 4,274,053 and U.S. Pat. No. 4,319,188; for example, disclose magnetic rotary encoders using a magnetic sensor made by a known magnetic resistance effect element (MR sensor) in the form of a thin sheet provided on a plate.
These magnetic rotary encoders are of great importance in the market of rotary detectors due to their advantages including a merit that the number of output pulses per revolution is obtained at a lower cost than in an optical rotary encoder.
One of the prior art magnetic circumference-reading rotary encoder is shown in FIG. 16 in a schematic form. In the same drawing, reference numeral 1 refers to a drum, 2 to a rotary shaft, 3 to a magnetized pattern, 4 to a magnetic sensor, 5 to a holding member and 6 to a chassis.
The drum 1 made from a magnetic material is driven by a motor or other means (not shown) rotatably about the rotary shaft 2, and has the magnetized pattern 3 provided on the circumferential surface thereof by a magnetic recording technology. The magnetized pattern 3 includes a number of separate parts spaced at an interval and aligned so that adjacent parts are opposite in polarity such as N, S, S, N, N, S, S, N, . . . . The magnetic sensor 4 is a known member made of magnetic resistance effect elements and is fixed on a sensor fixing surface 5a of the holding member 5 by an interval and aligned so that adjacent magnetic polarity adhesive or other means. The holding member 5 is made from aluminum or other metal or a synthetic resin material, and its bottom surface defines a mounting reference surface 5b which closely contacts a plane 6a of the chassis 6 when the holding member 5 is fixed to the chassis by bolts 7.
The magnetic sensor 4 is made of two magnetic resistance effect elements which are different in phase by np+1/4p (n is an integer) with respect to each magnetic polarity pitch p of the magnetized pattern 3 on the drum 1, and are opposed to the magnetized pattern 3 so that directions of magnetic paths of the magnetic resistance effect elements intersect with the rotary shaft 2 at a right angle. Therefore, when the drum 1 rotates, individual magnetic resistance effect elements of the magnetic sensor 4 produce signals which are different in phase by 90 degrees.
In the aforegoing magnetic rotary encoder, with one rotation of the drum 1 in a predetermined direction, individual magnetic resistance effect elements of the magnetic sensor 4 supply continuous signals having 90 degrees phase difference. Amplification, demodulation, matching or other signal processing are effected to the continuous signals to obtain incremental pulses which represent a movement and a rotating direction of the drum 1.
FIGS. 17 and 18 illustrate one form of prior art magnetic end-surface reading rotary encoder. In these drawings, reference numeral 1 refers to a disk, 2 to a rotary shaft, 3 to a magnetized pattern, 4 to a magnetic sensor, 5 to a holding member, 6 to a case, 7 to a bolt, and 14 to a bearing.
The disk 1 made from a magnetic material is rotatable about the rotary shaft 2 supported on the case 6 via the bearing 14. A planar disk surface 1a of the disk 1 is provided with the magnetized pattern 3 formed by a magnetic recording technology. As shown in FIG. 18, the magnetized pattern 3 includes a number of separate parts spaced at an pairs are opposite in polarity such as N, S, S, N, N, S, S, N . . . . The magnetic sensor 4 is a known member made of magnetic resistance effect elements, for example, and fixed on a sensor fixing surface 5a of the holding member 5 by an adhesive or other means. The holding member 5 is made from aluminum or other metal or a synthetic resin material, and its bottom surface defines a mounting reference surface 5b which contacts a plane 6a of the case 6 when the holding member is fixed to the case 6 by the bolts 7. The plane 6a is shaped to be parallel to a circumferential surface of a hole 6b when the hole 6b is formed in the center of the case 6, and an accurate parallel relationship is established between the surfaces in a relatively easy fashion. Therefore, a high accuracy is established in the parallel degree between the plane 6a and the rotary shaft 2 supported by the bearing 14 engaging the hole 6b, i.e. in the right angle degree between the plane 6a and the disk surface of the disk 1.
The magnetic sensor 4 is made of two magnetic resistance effect elements which are different in phase by np+1/4p (n is an integer) with respect to each magnetic polarity pitch p of the magnetized pattern 3 on the disk 1 and are opposed to the magnetized pattern so that directions of magnetic paths of the magnetic resistance effect elements intersect with the rotary shaft 2 at a right angle. Therefore, when the disk 1 rotates, individual magnetic resistance effect elements of the magnetic sensor 4 produce signals which are different in phase by 90 degrees.
In the aforegoing magnetic rotary encoder, with one rotation of the disk 1 in a predetermined direction, individual magnetic resistance effect elements of the magnetic sensor 4 supply continuous signals having 90 degrees phase difference. Amplification, demodulation, matching or other signal processing are effected to the continuous signals to obtain incremental pulses which represent a movement and a rotating direction of the disk 1.
In the magnetic circumference-reading rotary encoder, it is necessary to maintain a uniform distance and parallel relationship between the magnetic sensor 4 and the circumferential surface of the drum 1 carrying the magnetized pattern 3. If they are slanted by an angle .theta..sub.1 shown in FIG. 19 or by an angle .theta..sub.2 shown in FIG. 20, the output of the magnetic sensor 4 drops, and unables an accurate positional detection. For this reason, high accuracies are required in the right angle arrangement between the plane 6a and the sensor fixing surface 5a of the bolding member 5 and in the evenness of the mounting reference surface 5b of the holding member 5.
In this connection, prior art technologies sometimes effect a cutting operation to aluminum or other metal material to make up the sensor fixing surface 5a and mounting reference surface 5b of the holding member 5, or sometimes make an approximate outer configuration by die-casting or injection molding and thereafter effect a cutting operation or other secondary working to finish the sensor fixing surface 5a and the mounting reference surface 5b of the holding member 5.
The prior art technologies, however, involve various problems that it is difficult to uniform the finished configurations of the sensor fixing surface 5a and the mounting reference surface 5b, that any unevenness of the finished mounting reference surface 5b, for example, causes an angular error of the holding member 5 fixed by the bolts 7 and the magnetic sensor 4 fixed on the holding member 5, and that a significant time required for the finishing operation causes an increase of the manufacturing cost.
Focusing at the time required for the finishing operation among other problems, one proposal to reduce the finishing time is to effect punching, bending or other press operation to a metal plate to make the holding member 5. However, a simple pressing operation cannot establish a sufficient finishing accuracy in the same degree as in the cutting operation, due to a spring-back after a bending operation. It is desired to establish finishing accuracies of the sensor fixing surface and mounting reference surface of the holding member by manufacturing the holding member by press-cutting operation.
Also in the magnetic end-surface-reading rotary encoder, it is necessary to maintain a uniform distance and a parallel relationship between the magnetic sensor 4 and the disk surface 1a of the disk 1 carrying the magnetized pattern 3. If the parallelism between the disk surface 1a and the magnetic sensor 4 inclines by an angle .theta..sub.1 as shown in FIG. 19, or if the center line of the magnetized pattern 3 inclines by an angle .theta..sub.2 with respect to the azimuth angle of the magnetic sensor 4 as shown in FIG. 20, the output of the magnetic sensor 4 drops, and unables an accurate positional detection. For this reason, high accuracies are required in the right angle relationship between the plane 6a and the sensor fixing surface 5a of the holding member 5 and in the evenness of the mounting reference surface 5b of the holding member 5.
In this connection, prior art technologies sometimes effect a cutting operation to aluminum or other metal material to make up the sensor fixing surface 5a and mounting reference surface 5b of the holding member 5, or sometimes make an approximate outer configuration by die-casting or injection molding an thereafter effect a cutting operation or other secondary working to finish the sensor fixing surface 5a and the mounting reference surface 5b of the holding member 5.
The prior art technologies, however, involve various problems that it is difficult to uniform the finished configurations of the sensor fixing surface 5a and the mounting reference surface 5b, that any unevenness of the finished mounting reference surface 5b, for example, causes errors in the angle of the holding member 5 fixed by the bolt 7 and in the angle the magnetic sensor 4 fixed on the holding member 5, and that a significant time required for the finishing operation causes an increase of the manufacturing cost.
Focusing at the time required for the finishing operation among other problems, one proposal to reduce the finishing time is to effect punching, bending or other press operation to a metal plate to make the holding member 5. However, a simple pressing operation cannot establish a sufficient finishing accuracy in the same degree as in the cutting operation, due to a spring-back after a bending operation.
Additionally, Japanese Laying-Open Publication No. 60-72517 of a utility model application proposes to first mount the holding memher 5 on the plane 6a and thereafter correct the azimuth angle .theta..sub.2 shown in FIG. 21 by an azimuth adjusting mechanism. However, this requires a significant time and effort for azimuth adjustment, and is not suitable for mass-production. It is desired to establish finishing accuracies of the sensor fixing means and mounting reference surface of the holding member by manufacturing the holding member by press-cutting operation also in a magnetic end-surface-reading rotary encoder.
In respect of the holding member 5 of the magnetic rotary encoder, the magnetic sensor 4 produces angular errors .theta..sub.1 and .theta..sub.2 with respect to the surface carrying the magnetized pattern of the drum or disk used as a magnetic scale unless the sensor fixing surface 5a for adhesively fixing the magnetic sensor 4 is accurately even throughout the substantially entire surface thereof. Further, also when the sensor fixing surface 5a has a sufficient evenness, an uneven thickness of an adhesive used to fix the sensor fixing surface 5a and the magnetic sensor 4 causes the aforegoing angular errors .theta..sub.1 and .theta..sub.2. Additionally, the magnetic sensor 4 is normally made from glass or ceramic. Therefore, if the holding member 5 is made from metal, the sensor 4 is apt to drop from the holding member 5 due to a difference in thermal expansion coefficient therebetween. It is desired to eliminate angular errors .theta..sub.1 and .theta..sub.2 caused by unevenness of the sensor fixing surface 5a to adhesively fix the magnetic sensor 4 thereon or by uneven thickness of the adhesive, and also reliably hold the magnetic sensor 4 on the holding member 5 against a change in the temperature.